I can't figure out how to post a link on this garage talk app, but their's a book called Turbo Hydramatic 350 handbook by Ron Sessions. It's kind of the bible for do-it-yourself th350 work.
Whatever you do make sure you add a trans temp gauge. May look into a aftermarket cooler, but I've heard mixed reviews on them.

 

You are the second person that mentioned that book, so I went ahead and ordered it. I watched a really good video on Youtube. If the TH350 is easy, I'd hate to see hard. Still looks pretty intimidating, but I want to try anyway. I was going to get a rebuilt tranny anyway so worst case scenario is I still do, and I am out the money for the kit.